Re: [PATCH bpf-next 2/2] selftests/bpf: Add a test for arena range tree algorithm

[Jiri Olsa <olsajiri@gmail.com>]

On Thu, Nov 07, 2024 at 06:56:16PM -0800, Alexei Starovoitov wrote:
> From: Alexei Starovoitov <ast@kernel.org>
> 
> Add a test that verifies specific behavior of arena range tree
> algorithm and just existing bif_alloc1 test due to use
> of global data in arena.
> 
> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
> ---
>  .../bpf/progs/verifier_arena_large.c          | 110 +++++++++++++++++-
>  1 file changed, 108 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/bpf/progs/verifier_arena_large.c b/tools/testing/selftests/bpf/progs/verifier_arena_large.c
> index 6065f862d964..8a9af79db884 100644
> --- a/tools/testing/selftests/bpf/progs/verifier_arena_large.c
> +++ b/tools/testing/selftests/bpf/progs/verifier_arena_large.c
> @@ -29,12 +29,12 @@ int big_alloc1(void *ctx)
>  	if (!page1)
>  		return 1;
>  	*page1 = 1;
> -	page2 = bpf_arena_alloc_pages(&arena, base + ARENA_SIZE - PAGE_SIZE,
> +	page2 = bpf_arena_alloc_pages(&arena, base + ARENA_SIZE - PAGE_SIZE * 2,
>  				      1, NUMA_NO_NODE, 0);
>  	if (!page2)
>  		return 2;
>  	*page2 = 2;
> -	no_page = bpf_arena_alloc_pages(&arena, base + ARENA_SIZE,
> +	no_page = bpf_arena_alloc_pages(&arena, base + ARENA_SIZE - PAGE_SIZE,
>  					1, NUMA_NO_NODE, 0);
>  	if (no_page)
>  		return 3;
> @@ -66,4 +66,110 @@ int big_alloc1(void *ctx)
>  #endif
>  	return 0;
>  }
> +
> +#if defined(__BPF_FEATURE_ADDR_SPACE_CAST)
> +#define PAGE_CNT 100
> +__u8 __arena * __arena page[PAGE_CNT]; /* occupies the first page */
> +__u8 __arena *base;
> +
> +/*
> + * Check that arena's range_tree algorithm allocates pages sequentially
> + * on the first pass and then fills in all gaps on the second pass.
> + */
> +__noinline int alloc_pages(int page_cnt, int pages_atonce, bool first_pass,
> +		int max_idx, int step)
> +{
> +	__u8 __arena *pg;
> +	int i, pg_idx;
> +
> +	for (i = 0; i < page_cnt; i++) {
> +		pg = bpf_arena_alloc_pages(&arena, NULL, pages_atonce,
> +					   NUMA_NO_NODE, 0);
> +		if (!pg)
> +			return step;
> +		pg_idx = (pg - base) / PAGE_SIZE;

hi,
I'm getting compile error below with clang 20.0.0:

      CLNG-BPF [test_progs] verifier_arena_large.bpf.o
    progs/verifier_arena_large.c:90:24: error: unsupported signed division, please convert to unsigned div/mod.
       90 |                 pg_idx = (pg - base) / PAGE_SIZE;

should we just convert it to unsigned div like below?

also I saw recent llvm change [1] that might help, I'll give it a try

jirka


[1] 38a8000f30aa [BPF] Use mul for certain div/mod operations (#110712)
---
diff --git a/tools/testing/selftests/bpf/progs/verifier_arena_large.c b/tools/testing/selftests/bpf/progs/verifier_arena_large.c
index 8a9af79db884..e743d008697e 100644
--- a/tools/testing/selftests/bpf/progs/verifier_arena_large.c
+++ b/tools/testing/selftests/bpf/progs/verifier_arena_large.c
@@ -87,7 +87,7 @@ __noinline int alloc_pages(int page_cnt, int pages_atonce, bool first_pass,
 					   NUMA_NO_NODE, 0);
 		if (!pg)
 			return step;
-		pg_idx = (pg - base) / PAGE_SIZE;
+		pg_idx = (unsigned int) (pg - base) / PAGE_SIZE;
 		if (first_pass) {
 			/* Pages must be allocated sequentially */
 			if (pg_idx != i)